Wear resistant steel



Feb. 2, 1960 N. J. CULP WEAR RESISTANT STEEL Filed Feb. 20, 1958 :65; a zupwwza 006 G9? oqn United States Patent WEAR RESISTANT STEEL Neil J. Culp, West Lawn, Pa., assignor to The Carpenter Steel Company, Reading, Pa., a corporation of New Jersey Application February 20, 1958, Serial No. 716,433

6 Claims. (Cl. 75-125) This invention relates to wear resistant steel of relatively low total alloy content which is particularly suitable for use in making tools and dies. More particularly, the invention relates to a steel which can be readily hardened by quenching in oil or air from a relatively low hardening temperature such as 1450-1650" F. and which is extremely wear resistant in the hardened condition due to the presence of substantial quantities of mono-tungsten carbide (WC) particles in the hardened matrix.

Most of the commonly used high speed steels have good wear resistance derived from presence of relatively large total amounts of alloying elements such as chromium, vanadium, tungsten and molybdenum. Such steels contain mixtures of double carbides and other complex carbides of one or more of theseelements. It has been known for some time, however, that the mono-carbide of which can be easily hot-worked, which can be readily annealed, which can be machined easily in the annealed state, and which has a relatively low total alloy content, preferably below 10%. I

I have discovered that the foregoing objects can be achieved with a steel of the following composition:

(The sum of the chromium and molyb- 'denum contents should be at least 1% of the alloy.) The balance principally all iron.

The proper balance of carbon and tungsten is necessary in the foregoing composition in order to achieve the desired results. As a practical matter, the carbon content should not exceed about 2.5% because larger quane tities of' carbon make the alloy extremely difficult to hot work. I have found that a certain relationship of carbon tungsten imparts greater surface wear resistance to an alloy than is imparted by these more complex carbides. For example, cutting tools made of a sintered composition containing mono-tungsten carbide as the wear resistant element have proven superior to ordinary high speed steels. for tool and die purposes is in the high cost, due to the necessity of using complex manufacturing operations, or,

large amounts of expensive alloying elements, or both.

Attempts have'been made to produce 'wear resistant steels containing the superior mono-tungsten carbide in an alloy of relatively low total alloy content. Such efforts heretofore have been subject to one or more difficulties. For example, the simplest such alloy, a steel containing 1.3% carbon and 3.5 tungsten, cannot be hardened satisfactorily in air or oil in sizes larger than A diameter round. Water quenching is avoided for hardening such steels because of the likelihood of cracking, distortion and changes in dimension brought about by this quenchng method. added to try to rectify this objection, the result has usually been a loss of the maximum wear resistance because the carbides were converted to the more complex types rather than retaining the tungsten as the desirable mono-tungsten carbide. Industry has turned to addition of vanadium which readily forms vanadium carbide, and such alloys are more easily hardened but their wearresistance is not equal to that obtainable by the presence of mono-tungsten carbide. In addition, all ofsuch alloys with which I am familiar have a very high total alloying content and usually must be hardened by quenching from excessively high temperatures.

It is an object of this invention to provide a wear resistant steel, deriving superior wear resistance from the presence of substantial quantities of mono-tungsten carbide in a hardened ferrous matrix. It is a further object to provide such a steel that can be hardened to a Rockwell hardness on the C scale (R0) of at least 60 at the center of a 4" round section, by quenching in oil from a temperature in the range of 14501650 F.

Other objects are to provide such a wear resistant steel which can be satisfactorily hardened by air quenching,

A disadvantage of these sintered products When other elements have been.

and tungsten is necessary in such an alloy if substantial quantities of monotungsten carbide are to be formed and retained in the hardened matrix. The minimum amounts of carbon required for given amounts of tungsten, to form and retain the mono-tungsten carbide in the alloy, have been plotted on the graph, in the drawing. Curve X on this graph represents in general the minimum requirements for tungsten and carbon contents in alloys of my invention. For example, such an alloy containing 4% tungsten requires 1.3% or more of carbon in order to retain the wear resistant WC in the matrix.- Likewise, an alloy of my invention containing 1.7% carbon should also contain at least 1.9% of tungsten 'to achieve the desired properties. t

These minimum carbon and tungsten requirements are varied somewhat by changes in the amounts of manganese, chromium and/or molybdenum in the alloy. In general, the minimum amount of carbon is higher for a given quantity of tungsten as the proportions of chromium and molybdenum are increased. A decrease in the manganese content of the alloy will also raise this curve somewhat. To illustrate these effects, I have also plotted in the drawing acurve Y'which represents the minimum carbon and tungsten requirements when the alloy contains approximately 2% manganese, 1% chromium and, 1% molybdenum. This a minimum carbontungsten curve Y is changed only slightly by varying the molybdenum content of the alloy. Lowering the ChI'Oe mium content, however, has a' more pronounced effect as shown by curve X which represents the minimum carbon and tungsten contents required for an alloy contain ing 2% manganese, 1% molybdenum and only a residual few hundredths of 1% chromium.

While satisfactory alloys with respect to'hardness and wear resistance can be made with amounts of tungsten up to 10%, little or no advantage is gained by the use of the larger amounts of tungsten. Amounts of tungsten above 6 to 7% also may make the alloy diflicult to hot work. Accordingly, I prefer to use from about 2% to 6% tungsten in the alloy.

' this element. Within the preferred range'of 1.5 to 2.5

for manganese, the alloys of my invention contain in the hardened state particles of tungsten carbide of substantial size. I have found that the larger sizes of these carbide particles in the matrix produce better wear resistance than smaller particles, although, of course, other factors being equal, wear resistance is improved by the presence of a larger total volume of monotungsten carbide particles.

The elements chromium and molybdenum have an important, although lesser, effect on hardenability than manganese. These elements have a substantial effect, however, on tungsten carbide formation and if present in too large quantities result in the production of the complex tungsten carbides instead of the desired monotungsten carbide. When larger amounts of manganese are present within the range given above, the desired hardenability of the alloy can be obtained with smaller quantities of chromium and molybdenum. .These latter elements each affect the hardenability of the alloy in much the same way so that suitable alloys can be made containing only a residual amount of chromium such as 0.05% or with only a residual amount such as 0.05% of molybdenum. I prefer, however, that the sum of the chromium and molybdenum contents shall be at least 1%.

It is desirable to exclude from the alloy any more than traces of strong carbide forming elements such as vanadium, titanium, zirconium, columbium or tantalum. Other elements that are not strong carbide formers may be present in small quantities without destroying the basic properties of the alloy. Copper may be used in an amount not exceeding 3%. Residual amounts of nickel or cobalt can be tolerated although it is best not to include more than 0.5% of one of these elements. Likewise silicon, if present, should not exceed about 1% in amount.

The following examples of alloys are given as illustrative of my invention and not by way of limitation.

Example 1.--An alloy of my preferred analysis was melted in the usual manner and cast into ingot shape. This preferred analysis was as follows in terms of percent by weight.

elements in the amounts normally found as impurities in such steels.

The ingot was readily forged and worked at a temperature of about 1950-2000 F., and the alloy was readily annealed. In the annealed state, the specimens exhibited a spheroidized structure, were easily machined and had a Brinell hardness of the order of 240 to 270. When oil quenched from 1450" F., the alloy, even in sections up to 8 inches in diameter had a hardness of Re 64-66. When air hardened from 1550 F., the alloy attained a hardness of R 63-64 although only in sections up to about 4 inches in diameter. The alloy is normally used after hardening and tempering at a temperature of 300 to 350 F., in which state it has a hardness of about Rc 63-65.

Wear resistance was determined on prepared samples 0.875" in diameter by 1" in length which were moved by an eccentric arm radially over the face of a revolving disc 9." in diameter covered with 120 grit Alundum Jewelox cloth. The disc was rotated at the rate of 25 r.p.m. for l000'revolutions during which time the specimen was moved back and forth 83 /2 times. The measure of wear resistance was the weight lost by the specimen in grams during this test. For this particular alloy, the weight loss was found to be .025/.03 gram.

This alloy has been found to be excellent for tool and die use such as plungers in a Denison press, as shear blades and as punches operating against beryllium copper and stainless steel sheets.

. of R0 64 in sections 1 inch in diameter.

4 Example 2.-An alloy was melted and cast having the following analysis:

- Percent Carbon 1.83

Manganese 2.38 Chromium 1.66 Molybdenum 1.05 Tungsten 3.69 Silicon 0.47 Iron Balance, except for impurities.

Percent Carbon 1.85 Manganese 1.46 Chromium 1.14 Molybdenum 1.05 Tungsten 3.93 Iron Balance, except for silicon and impurities.

This alloy, when oil quenched from 1500 F. had a hardness of Re 64 in sizes up to 2 inches in diameter, and when air quenched from 1600 F. had a hardness Its Wear resistance, as measured by the test outlined above was excellent, the weight loss of the samples being 0.0200.023 gram.

Example 4.-An alloy of the following analysis was melted and cast:

- impurities.

This alloy, when oil quenched from 1500 F. had a hardness of Re 64 in sizes up to 2 inches in diameter, and when air quenched from 1600 F. had a hardness of 61/62 in sizes up to 1 inch in diameter. It was found to be readily hot worked and easily annealed, with good machineability in the annealed state.

When oil quenched and tempered, specimens of the alloy showed goodwear resistance in the above test, the Weight loss varying from 0.022 to 0.039 gram at hardness of Re 65 to 60, respectively.

The terms and expressions which I have employed are used as terms of description and not of limitation, and I have no intention, in the use of such terms and expressions, of excluding any equivalents of the features shown and described or portions thereof, but recognize thatvarious modifications are possible within the scope of the invention claimed.

I claim:

1. A wear resistant steel oil hardenable to at least R0 60 with substantial amounts of mono-tungsten carbide particles in the hardened matrix, said steel containing about 1 to 2.75% manganese, about 0.05 to 1.8% chromium, about 0.05 to 1.5% molybdenum, the sum of the chromium and molybdenum contents being at least 1%, about 1.0 to 2.5% carbon, about 1.3 to 10% tungsten, and the balance essentially iron, the proportions of tungsten and carbon falling on or above the curve X on the graph of the d a i 2. A wear resistant steel containing about 1.5 to 2.5% manganese, 0.05 to 1.5% chromium, 0.05 to 1.3% molybdenum, the sum of the chromium and molybdenum contents being at least about 1%, 1.3 to 2.5 carbon, 2 to 6% tungsten, and the balance essentially iron, the proportions of carbon and tungsten falling on 01' above the curve X on the graph of the drawing.

3. A tool and die steel alloy that is readily machinable in the annealed state and is hardenable by oil and air quenching to form a hardened matrix containing substantial quantities of wear resistant mono-tungsten carbide particles, said steel containing about 1 to 2.75% manganese, about 0.05 to 1.8% chromium, about 0.05 to 1.5% molybdenum, the sum of the chromium and molybdenum contents being at least 1%, about 1.0 to 2.5 carbon, about 1.3 to 10% tungsten, and the balance essentially iron, the proportions of tungsten and carbon falling on or above the curve X on the graph of the drawmg.

4. Wear resistant steel containing 1.5 to 2.5% manganese, 0.5 to 1.5% chromium, 0.5 to 1.3% molybdenum, 1.4 to 2.5% carbon, 3 to 5% tungsten, and the balance substantially all iron. I

5. Wear resistant steel having the following analysis within the tolerances of good melting practice:

6. An alloy steel as defined in claim 1 which also contains copper in a definite amount not exceeding 3%.

References Cited in the file of this patent UNITED STATES PATENTS 1,496,980 Armstrong June 10, 1924 

1. A WEAR RESISTANT STEEL OIL HARDENABLE TO AT LEAST RC 60 WITH SUBSTANTIAL AMOUNTS OF MONO-TUNGSTEN CARBIDE PARTICLES IN THE HARDENED MARTIX, SAID STEEL CONTAINING ABOUT 1 TO 2.75% MANGANESE, ABOUT 0.05 TO 1.8% CHROMIUM, ABOUT 0.05 TO 1.5% MOLYBDENUM, THE SUM OF THE CHROMIUM AND MOLYBDENUM CONTENTS BEING AT LEAST 1%, ABOUT 1.0 TO 2.5% CARBON, ABOUT 1.3 TO 10% TUNGSTEN, AND THE BALANCE ESSENTIALLY IRON, THE PROPORTIONS OF TUNGSTEN AND CARBON FALLING ON OR ABOVE THE CURVE X ON THE GRAPH OF THE DRAWING. 